Monthly Archives: November 2009

Post navigation

Charles Darwin’s groundbreaking work, The Origin of Species, was published 24 November, 1859, 150 years ago today. This makes a rather neat bookend to the Darwin Bicentenary, the year of events commemorating the 200th anniversary of Darwin’s birth on 12 February, 1809. I’m going to be lazy and simply link to everything I wrote back concerning that earlier anniversary.

Oh, and serendipitously, today is also the anniversary of the discovery of Lucy in 1974. I saw her in person (behind glass) on a trip to Seattle during last year’s fall break, which was pretty cool.

Most aphid species produce some sort of sweet honeydew as waste while feeding on their host plants; ant-attended aphid species use this honeydew to attract ants. In many cases, the ants “milk” the aphids by stroking them to prompt release of the honeydew. While exploiting a colony of aphids, ants defend it as a food resource, protecting the aphids from predators. Aphid species that commonly rely on ant protection often lack defensive adaptations [$-a] found on species that don’t interact with ants.

Niesen et al. report the results of experiments performed ants attending colonies of milkweed aphids, Aphis asclepiadis, which are susceptible to a fungal pathogen that can wipe out aphid colonies in a matter of days. In two experiments, they introduced aphids into the ant-attended colonies, and tracked what the ants did to them. They found that

Ants were more likely to remove the corpses of fungus-killed aphids than either the corpses of aphids killed by freezing or introduced live aphids; and

Ants were more likely to remove live aphids contaminated with fungal spores (conidia) than live aphids without spores.

The authors speculate that this behavior is a re-application of ants’ treatment of their own sick and dead within the colony. It seems clear that it should have benefits to both ants and aphids in this new context, slowing or preventing the spread of the fungus within an aphid colony. This benefit isn’t directly tested by Nielsen et al., but such an experiment is a logical next step.

Citing the Rev. Dr. Martin Luther King Jr.’s call to civil disobedience, 145 evangelical, Roman Catholic and Orthodox Christian leaders have signed a declaration saying they will not cooperate with laws that they say could be used to compel their institutions to participate in abortions, or to bless or in any way recognize same-sex couples.…They say they also want to speak to younger Christians who have become engaged in issues like climate change and global poverty, and who are more accepting of homosexuality than their elders. They say they want to remind them that abortion, homosexuality and religious freedom are still paramount issues.

This, of course, is on the heels of the threat by the Roman Catholic Archdiocese of Washington, D.C. to discontinue charitable work if the city council passes a law prohibiting discrimination on the basis of sexual orientation.

Christianity was founded on stories of a man who preached sacrifice of self to the needs of others, went drinking with prostitutes and other social outcasts, and was executed as a common criminal by the government. The figure of Jesus as described in the Christian scriptures is, to me, an ideal I can only hope to emulate. Yet many of the people who take his name for their moral identity — and the loudest, most vehement and visible of those who do — would evidently react with disgust if they met their Lord on the street, and condemn his teachings as un-American if they actually understood them.

I wanted to write something more scathing than that. But I’m just tired. I’m going to hand the mic over to that guy they keep claiming to follow.

Woe to you, teachers of the law and Pharisees, you hypocrites! You shut the kingdom of heaven in men’s faces. You yourselves do not enter, nor will you let those enter who are trying to. …Woe to you, teachers of the law and Pharisees, you hypocrites! You give a tenth of your spices — mint, dill and cummin. But you have neglected the more important matters of the law — justice, mercy and faithfulness. You should have practiced the latter, without neglecting the former.…Woe to you, teachers of the law and Pharisees, you hypocrites! You are like whitewashed tombs, which look beautiful on the outside but on the inside are full of dead men’s bones and everything unclean. In the same way, on the outside you appear to people as righteous but on the inside you are full of hypocrisy and wickedness. …You snakes! You brood of vipers! How will you escape being condemned to hell?(Matthew, chaper 23, New International Version.)

Among birds, brood parasites are the ultimate freeloaders — species like the common cuckoo and the brown-headed cowbird lay their eggs in other birds’ nests, leaving the host to raise the parasite chicks at the expense of its own. But while brood parasitism is easy on the parents, it isn’t so easy on their chicks, as a study recently published in PLoS ONE suggests.

A brood parasitic chick faces two challenges. The first is to avoid being recognized by its adoptive parents and ejected from the nest; the second is to win parental attention in competition with their adoptive nest-mates. The first challenge may be partially met by the evolution of eggshells that match host eggshells; and brood parasite parents may also help by keeping watch on the host nest so they can punsish hosts who eject introduced eggs. (This punishment behavior has been described as an “avian mafia [$-a].”)

In competition with their adoptive nest-mates, though, parasitic chicks are on their own. If the host’s own eggs hatch, the host has more mouths to feed and less time to spend on the parasitic chick. On the other hand, a brood parasitic mother can’t kick out the host’s eggs at the time she leaves her own egg with the host, because the host may abandon a nest that contains only a single unfamiliar-looking egg. This leaves it to freshly-hatched brood parasite chicks to do the heavy lifting involved in ejecting their host’s eggs themselves.

A common cuckoo chick pushes one of its host’s eggs out of the nest. Detail of figure 1 from Anderson et al. (2009).

Egg eviction looks like hard work — the chicks attempt it while they’re not much bigger than the eggs. Anderson et al. investigated the cost of all this adoptive-siblicidal effort by manipulating reed warbler nests that had been parasitized by common cuckoos,* taking away the hosts’ eggs in experimental nests, and comparing the growth of cuckoo chicks in those nests to that of chicks in unmanipulated nests, who had to do the evicting themselves.

They found that there is a cost to eviction effort: during the period of development when they would be doing all they could to push eggs out of the nest, cuckoo chicks grew faster when they didn’t have eggs to push. But they didn’t grow much faster, and by the time they were ready to leave the nest, the advantage had disappeared. Anderson et al. take this to mean that the cost of eviction is “recoverable” through the benefits of increased parental attention later on. I would add that it points out how important your choice of time frame can be when investigating how traits or behaviors affect organisms’ evolutionary fitness — sometimes a cost paid at one point in development is an investment toward later benefits.

——–*The common cuckoo is the species first known to parasitize other birds’ nests, and its name is the linguistic source of the term “cuckold.”

Hey, Proceedings of the National Academy of Sciences? (Can I call you PNAS? Thanks.) You know what really drives me crazy, as a scientist and a blogger, PNAS? Internationally-recognized journals that release scientific studies to the press before they make them available online.

Why does this make me crazy? I’m glad you asked, PNAS. It makes me crazy because sometimes I read something as batshit absurd as this gem from Wired Science:

No exact rule exists for deciding when a group of animals constitutes a separate species. That question “is rarely if ever asked,” as speciation isn’t something that scientists have been fortunate enough to watch at the precise moment of divergence … [emphasis mine]

(Which statement is like claiming that physicists rarely ask about gravity.) And when I read something like this I’d really like to be able to go and see whether that’s actually in the peer-reviewed article in question, or if it just materialized in the course of the sausage-making that is popular science journalism.

But, apparently, PNAS, you’re more interested in having your results butchered by people who think biologists don’t ask questions about speciation than you are in having them read by, you know, biologists. You’ll forgive me, I hope, if I take that a little bit personally.

First, the match between the Joshua tree flowers and the moths’ ovipositors suggested that coevolution might have molded the relationship between the plant and the pollinator. Second, because the plants are completely dependent on the moths for reproduction, the differences in the flowers might have caused Joshua trees to split into two different species.

Prior to the origins of modern flowering plants, or angiosperms, in the early-middle Cretaceous period, most of the diversity of land plants were gymnosperms. These plants are characterized by “naked seeds” — reproductive organs exposed to the air, where the wind can catch pollen and carry it from one plant to fertilize the ovules of another. In a world dominated by gymnosperms, the thinking used to be, animal pollinators were mostly unnecessary.

The new paper by Ren et al. challenges this idea with the description of a set of fossilized scorpionflies, all of which have strikingly long probosces that are clearly suited to sucking up liquid. The earliest of these fossils are from the Jurassic, tens of millions of years before the flowering plants began to diversify. In modern insects, sucking mouthparts like the ones described are associated with two kinds of feeding: drinking pollen, and drinking blood. To determine which was most likely in this case, Ren et al. performed energy-dispersive spectroscopy on the best-preserved fossil, and found no sign of the elevated levels of iron in the proboscis that would result from the residue of blood meals. This suggests that the scorpionflies were drinking nectar, or something like it.

Nectar has one major function in plants: to attract insects. Ant-protected plants reward their ants with nectar, and flowering plants use nectar to lure animal pollinators close enough to pick up or drop off pollen. If these ancient scorpionflies were, in fact, living on nectar, Ren et al. reason they were probably pollinating contemporary plants, which were all gymnosperms. The authors identify a diverse list of candidate host plants, including seed ferns and a relative of the modern ginkgo, whose reproductive structures were (1) too well-sheltered for efficient wind pollination or (2) included tubular structures similar to those that modern plants use to guide nectar-feeding pollinators. Finally, the authors point out, many modern gymnosperms produce “ovular secretions” that are very similar to the nectar produced by angiosperms.

As a neontologist, I’m often amazed how much can be told from million-years-old fossils — who knew there was a way to test for residual blood in a fossilized proboscis? At the same time, Ren et al. connect some mighty scattered dots to build their hypothesis. The real clincher is that it seems mighty unlikely that animal pollination would be rare in a world that already has both flying insects and pollen-producing plants. Animal pollination is much more efficient than wind pollination, and if there’s one constant in evolutionary history, it’s that living things rarely miss an opportunity like that.

Over on Slate, Rebecca Tuhus-Dubrow says some conservation biologists are starting to question the importance of preventing species invasions:

Certainly, they say, non-native plants and critters can be terribly destructive—the tree-killing gypsy moth comes to mind. Yet natives such as the Southern Pine Beetle can cause similar harm. The effects of exotics on biodiversity are mixed. Their entry into a region may reduce indigenous populations, but they’re not likely to cause any extinctions (at least on continents and in oceans—lakes and islands are more vulnerable). Since the arrival of Europeans in the New World, hundreds of imports have flourished in their new environments.

Tuhus-Dubrow cites the case of Tamarisk in the U.S. Southwest — an aggressive introduced shrub that has also ended up providing important nesting sites for the endangered southwestern willow flycatcher.

The fact of the matter is that human-introduced species can eventually integrate into an ecological community; once they do it’s hard to get them out, and problematic as to whether it’s a good idea. In Australia, dingoes helped extirpate many other large predators when they were introduced by the first humans to arrive on that continent — and now they’re critical to controlling other, later-introduced mammal species.

Mike Konczal considers the effect of breaking Defense Department spending out as a separate line item on pay stub tax witholding statements, alongside Social Security and Medicare. If citizens saw a number for military alongside social spending, they might make more informed choices about the relative values of each.

How much of your two weeks work cycle would you like to spend working to keep a global military hegemony going? I’d probably want to clock it out around my first coffee break on Monday (which is fairly early), but that’s me.

Some pacifists withhold a portion (or all) of their Federal taxes in protest against military spending, and there’s even a campaign to let people opt out of funding the military on their tax forms. Maybe Konczal’s idea would be a good alternative?